KRAS and neoplasm: Anti-YFP staining of the R26YFP;p53fl/fl;Kras;Lfng-RFP/CreER (R26YFPPKC-Lfng) pancreas was positive in all tumor cells (Fig. 2N) and negative in native duct (arrowhead in Fig. 2O), confirming that tumor cells had originated from Lfng-expressing cells.